The present invention relates to apparatus for the assembly/disassembly of a turbofan gas turbine engine and, more particularly, to an apparatus for removably attaching a core frame to a vane frame with a stable mid ring.
Turbofan gas turbine engines generally include a core engine coupled in driving relationship to a forward mounted fan module. The fan module, in a high-bypass ratio engine, includes a large diameter single stage fan and a multiple stage intermediate pressure compressor or booster. The fan is surrounded by a fan casing supported by a plurality of structural members compositely referred to as a vane frame, which frame is supported on a hub frame extending from the core engine. The core engine includes a high pressure compressor, a combustor, and a multi-stage turbine for extracting energy from combustion gases exiting the combustor for driving the compressors and fan.
Mounting of such high-bypass engines on an aircraft generally requires one or more structural supports which connect the engine to a structural member, sometimes referred to as a strut or pylon, on a wing or fuselage, depending upon the mounting location. The structural supports extend through an aerodynamic cowling, sometimes referred to as a nacelle, and couple to the engine core frame. Coupling may be to the fan casing (or shroud) and to the casing surrounding the turbine. In general, some form of structural yoke is attached to the engine casing and some structural supports attach to the yoke.
As gas turbine engines have become more powerful and larger, a concern has developed with handling and transporting of such engines. In particular, engines are now being developed with fans and fan casings having diameters in the range of twelve feet. Transporting of such engines by air or ground is not practical with current commercial aircraft and over-the-road transportation guidelines. Accordingly, it is desirable to provide a method of assembly and disassembly of such engines which permits transport without exceeding aircraft or ground transport size limitations.
The problems associated with handling and transporting of such large engines extends beyond shipments to the installation, removal, and handling of the engines in aircraft servicing. It is therefore further desirable to provide a method and apparatus for servicing of such engines which overcome the problems associated with such large diameter fans.
In the aforementioned U.S. patent application Ser. No. 07/708,263, one of the connection points between the hub frame and vane frame is shown as a mid ring connection. The combined frames are attached to an aft fan case. The core structure or hub frame, out to a radius of approximately twenty-nine inches, is preferably a one piece casting. A ring with an inner radius of approximately twenty-nine inches and outer radius of approximately thirty-five inches is welded onto the hub frame casting structure making it a one piece fabricated hub structure. Bypass vanes are attached to a vane frame structure at its inner diameter ring of approximately thirty-five inch radius and extend to an outer ring of approximately sixty-three inches radius. The vane frame inner ring and the hub frame outer ring are joined to form a separable joint which defines a mid ring relative to the fan frame assembly. Consequently, this separable joint or the ring portions thereof, whether the hub frame outer ring or the vane frame inner ring, are interchangeably known as the mid ring.
The mid ring separable joint is composed of a forward flange joint and an aft flange joint. Since the forward joint and the aft joint have space limitations, they are at or nearly at the same radius. To remove the hub frame, with the core engine attached, the hub frame is required to move aft leaving the vane frame with the vane nacelle which may or may not remain with the aircraft. Consequently, the forward mid ring flange of the hub frame must pass through the aft mid ring flange of the vane frame. Accordingly, some method must be provided for accomplishing this function.
In addition, the core struts extend into the hub frame mid ring where the walls flare into flat panels. These flat panels are interrupted by large holes which help to isolate the weld joints from the rest of the structure. The flat panels, extending from the front to the aft mid ring flanges, may not be stable under expected shear forces. Thus, a more stable hub frame structure is needed. Furthermore, there is a concern that the tolerance accumulations between the front flange and the aft flange in the axial direction may not be accommodated without excessive stress being generated in the flange fasteners and the flange structure at assembly.